BAEN/625
Fall/2010
RGM
Homework # 5
Biological and Agricultural Engineering
Texas A&M University
Due date: March 8, 2010
1) A parallel beam of 1.35 MeV electrons is normally incident on a 10 leaves of (1 mm
thick/each) spinach ( = 915 kg/m3). Assume the leaves are stacked together with no-air in
between. Answer the following questions.
(a) Plot the MCSP and MRSP [MeV cm2/g] against electron energy [MeV] from 0.01-20
MeV for the spinach leaf
(b) What is the range of the electrons in the spinach?
(c) Calculate the mean excitation energy of spinach.
2) Assume that a 150 g spinach is placed inside a plastic bag made of 15m-thick Mylar ( = 850
kg/m3). The total sample thickness is around 8.2 cm and bulk density of spinach bag is b = 525
kg/m3. How much energy do the electrons need to penetrate the entire sample? The maximum
allowed by the FDA is 10 MeV.
3) A producer wants to irradiate cantaloupes for disinfestations (surface only) treatment using
e-beam. The processing facility has two 10 MeV LINAC accelerators that can operate in a single
(top or bottom) mode or double-mode. To reduce the e-beam energy, so the penetration is
only 1 cm deep, the processor needs to use a shield (in this case Lucite plastic). Consider the
sketch of a cantaloupe being irradiated with electrons as shown in the Figure below and the
density distribution within the product. Assume the cantaloupe spherical with a radius of 7.2
cm and density of 920 kg/m3. Consider a single beam striking the product’s surface.
(a) Calculate the Lucite thickness needed to reduce the 10-MeV e-beams to the desired
energy to treat the fresh cantaloupe.
(b) Plot the MSP for the cantaloupe and Lucite